Method for determining location of power feeding point in electroplating apparatus and electroplating apparatus for plating rectangular substrate

ABSTRACT

To optimize a location of a power feeding point with the use of a square substrate. There is disclosed a method for determining a location of a power feeding point in an electroplating apparatus. The electroplating apparatus is configured to plate a rectangular substrate having a substrate area of S. The rectangular substrate has opposed two sides coupled to a power supply. The rectangular substrate has a length L of the sides coupled to the power supply and a length W of sides not coupled to the power supply meeting a condition of 0.8×L≤W≤L. The method includes determining a number N of the power feeding points according to the substrate area S.

TECHNICAL FIELD

The present invention relates to a method for determining a location ofa power feeding point in an electroplating apparatus and theelectroplating apparatus for plating a rectangular substrate.

BACKGROUND ART

A method for forming a metal film and/or an organic film on a substratesuch as a wafer by a plating process has been recently employed inwiring of a semiconductor circuit and a method for forming a bump. Thefollowing method has been widely employed. For example, a gold, anargentum, a copper, a solder, a nickel, or a wiring or a bump (aprojecting coupling electrode) formed by laminating these substances inmultilayer is formed at a predetermined part on a surface of the waferwhere the semiconductor circuits and a micro wiring coupling thesesemiconductor circuits together are formed. The wafer is coupled to anelectrode of a package substrate and/or a Tape Automated Bonding (TAB)electrode via this bump. While various methods such as an electroplatingmethod, an electroless plating method, a deposition method, and aprinting method are available as the method for forming these wiring andbump, in association with an increase in the number of I/Os of asemiconductor chip and a decrease in pitch, the electroplating methodconfigured to handle miniaturization and featuring a fast filmattachment speed has been often used. The metal film obtained byelectroplating currently most frequently used features high purity, afast film formation speed, and ease of a film thickness regulatingmethod.

A general electroplating apparatus couples a substrate to a negativeelectrode of a power supply, couples an anode to a positive electrode ofthe power supply, and applies a voltage between the anode and thesubstrate to form a metal film on the substrate. Here, as disclosed inJapanese Unexamined Patent Application Publication No. 2015-161028 (PTL1), there has been known that in the case where a power feeding portionis disposed only at a center of an anode, an electrical resistance ofthe anode generates a difference between a current at the center of theanode and a current at an outer peripheral portion of the anode. Thecurrent difference generated in the anode possibly adversely affectsuniformity of a thickness of the metal film formed on the substrate.

PTL 1 discloses an anode unit that includes a plurality of radiallyextending arms fixed to an outer peripheral portion of an anode. PTL 1discloses that, by supplying an electric power from the power feedingportion to the outer peripheral portion of the anode through theplurality of arms, the current will uniformly flow through the entireanode.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2015-161028

SUMMARY OF INVENTION Technical Problem

It is assumed that an electroplating with an anode unit of PTL 1, acurrent uniformly flows through an entire anode, and this results in acomparatively uniform plating thickness. However, PTL 1 does notdescribe optimum fixed positions between the anode and power feedingportions and the optimum number of fixation points in detail.Especially, PTL 1 does not clarify optimum fixed positions and theoptimum number of fixation points with the use of a square substrate.Therefore, one object of this application is to optimize a location of apower feeding point with the use of a square substrate.

Solution to Problem

This application discloses a method for determining a location of apower feeding point in an electroplating apparatus as one embodiment.The electroplating apparatus is configured to plate a rectangularsubstrate having a substrate area of S. The rectangular substrate hasopposed two sides coupled to a power supply. The rectangular substratehas a length L of the sides coupled to the power supply and a length Wof sides not coupled to the power supply meeting a condition of0.8×L≤W≤L. The method includes determining a number N of the powerfeeding points according to the substrate area S. The power feedingpoints are points at which an auxiliary electrode electrically contactspower feeding elements. The auxiliary electrode is configured to assistthe plating on the substrate. The power feeding element is configured tosupply the auxiliary electrode with an electric power from the powersupply.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an electroplating apparatusaccording to a first embodiment;

FIG. 2 shows a result of an electric potential simulation of anauxiliary electrode when a power feeding point is present only at acenter of the auxiliary electrode;

FIG. 3 shows a result of a plating thickness simulation on a substratewhen the auxiliary electrode has an electric potential distributionillustrated in FIG. 2;

FIG. 4 shows a result of an electric potential simulation of theauxiliary electrode when power feeding points are present by threepoints on the auxiliary electrode;

FIG. 5 shows a result of a plating thickness simulation on the substratewhen the auxiliary electrode has an electric potential distributionillustrated in FIG. 4;

FIG. 6A shows profiles of film thicknesses on lines drawn from centersof the substrates along lateral directions in the simulations of FIG. 3and FIG. 5;

FIG. 6B shows profiles of film thicknesses on lines drawn from thecenters of the substrates along upper/lower directions in thesimulations of FIG. 3 and FIG. 5;

FIG. 6C shows profiles of film thicknesses on lines drawn from thecenters of the substrates along diagonal directions in the simulationsof FIG. 3 and FIG. 5;

FIG. 7 is a drawing of the auxiliary electrode illustrating positionswhere the power feeding point can be provided;

FIG. 8 is a cross-sectional view of the electroplating apparatusaccording to a second embodiment; and

FIG. 9 is a front view of an auxiliary electrode holder according to thesecond embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 1 is a cross-sectional view illustrating an electroplatingapparatus 100 according to the first embodiment. Note that FIG. 1 andthe other drawings are schematic diagrams. Therefore, shapes,dimensions, positions, and similar specifications of components in thedrawings do not necessarily match shapes, dimensions, positions, andsimilar specifications of the actual components.

The electroplating apparatus 100 of this embodiment includes a platingtank 110. The plating tank 110 is provided to internally hold a platingsolution. The plating tank 110 preferably includes an overflow tank 120at the side portion of the plating tank 110, to catch the overflownplating solution from the plating tank 110. The plating tank 110 iscoupled to the overflow tank 120 with a circulation line 121. Theplating solution flown into the overflow tank 120 passes through thecirculation line 121 and returns to the inside of the plating tank 110.

The electroplating apparatus 100 includes a substrate holder 130 forholding a substrate 131 and for immersing the substrate 131 into theplating solution. The substrate holder 130 is configured so as toremovably and vertically hold the substrate 131. The substrate 131 ofthis embodiment has a square shape.

The electroplating apparatus 100 further includes an auxiliary electrodeunit 140. The auxiliary electrode unit 140 includes an auxiliaryelectrode 141 and a power feeding element 142 to supply an electricpower from a power supply 150 to the auxiliary electrode 141. Theauxiliary electrode unit 140 may include an auxiliary electrode holder(not illustrated) that holds the auxiliary electrode 141. Here,“auxiliary electrode” means “an electrode on which performing a platingis not intended,” in other words, “an electrode that assists theplating.” “An electrode on which performing the plating is intended,” inother words, “the electrode on which the plating is performed with theassistance by the auxiliary electrode” is the substrate 131. Generally,it can be said that the auxiliary electrode 141 is an electrode to whicha voltage having a polarity opposite to a polarity of a voltage appliedto the substrate 131 is applied.

The auxiliary electrode 141 is opposed to the substrate 131 at theinside of the plating tank 110. At least a part of the auxiliaryelectrode 141 is made of a material insoluble to the plating solution.Similarly to the substrate 131, the auxiliary electrode 141 is formedinto a square shape. In the following, a surface of the auxiliaryelectrode 141 opposed to the substrate 131 is referred to as “frontsurface” (a surface illustrated on the left in FIG. 1). Further, in thefollowing, a surface of the auxiliary electrode 141 on the side oppositeto the front surface is referred to as “back surface” (a surfaceillustrated on the right in FIG. 1).

The power feeding element 142 is fixed to the auxiliary electrode 141. Amethod for fixing the power feeding element 142 may be any given method,for example, a fixation with a fixture, a fixation by welding, or asimilar method is usable. The auxiliary electrode unit 140 may beconfigured such that a point where the auxiliary electrode 141electrically contacts the power feeding element 142 (hereinafterreferred to as “power feeding point 143”) is changeable. The auxiliaryelectrode 141 is coupled to the power supply 150 via the power feedingelement 142.

In FIG. 1, the power feeding point 143 is illustrated so as to beprovided by only one point in the center of the auxiliary electrode 141.However, as described later, the position of the power feeding point 143is not limited to the center of the auxiliary electrode 141. Similarly,the number of power feeding points 143 is not limited to one.

The substrate 131 is coupled to the power supply 150 via a componentsuch as a wiring or an electrode disposed at the substrate holder 130.In this specification, the component such as the wiring disposed at thesubstrate holder 130 is also regarded as a part of the substrate holder130. The substrate holder 130 holds the substrate 131 such that theopposed two sides of the substrate 131 are coupled to the power supply150.

In FIG. 1, the substrate 131 is illustrated so as to be coupled to anegative electrode of the power supply 150 and the auxiliary electrode141 is illustrated so as to be coupled to a positive electrode of thepower supply 150. Accordingly, the auxiliary electrode 141 is an anodein the example of FIG. 1. However, depending on conditions for theplating, the positive and the negative of the electrodes coupled to thesubstrate 131 and the auxiliary electrode 141 are possibly inverted (theauxiliary electrode 141 possibly serves as a cathode). The power supply150 may be configured integrally with the electroplating apparatus 100,that is, as a part of the electroplating apparatus 100. Alternatively oradditionally, an external power supply may be used as the power supply150.

The electroplating apparatus 100 can include, for example, a puddle 160to stir the plating solution and/or a mask 170 to adjust an electricpotential or a current inside the plating tank 110. The mask 170 has anopening 171. The electroplating apparatus 100 may further include otherelements including a pipe to supply the plating solution, aheater/cooler to adjust the temperature of the plating solution, andother elements.

The applicant performed the following two kinds of simulations tooptimize the location of the power feeding point 143. One simulation isan electrode potential simulation at the surface of the auxiliaryelectrode 141 under certain conditions. The other one simulation is aplating thickness simulation on the substrate 131 using the result ofthe electrode potential simulation of the auxiliary electrode 141. Theplating thickness simulation is performed with the optimum sized opening171 of the mask 170 under the respective conditions. Furthermore, exceptfor an interaction of the auxiliary electrode 141 with the power feedingelement 142 at the power feeding point 143, the electrode potentialsimulation does not consider an interaction of the auxiliary electrode141 with other elements (for example, the plating solution).Simultaneously with the simulation of the plating thickness, aninterface potential of the auxiliary electrode 141 with the platingsolution is simulated from the result of the electrode potentialsimulation of the auxiliary electrode 141.

FIG. 2 illustrates the result of the electrode potential simulation ofthe auxiliary electrode 141 when the power feeding point 143 is presentonly at the center of the auxiliary electrode 141. The auxiliaryelectrode 141 having an elongated rectangle shape with the length in theupper/lower direction of 510 mm and the lateral width of 415 mm wassimulated. Furthermore, the auxiliary electrode 141 was simulated as ageneral insoluble electrode. FIG. 2 illustrates the position of thepower feeding point 143 by the dotted line. FIG. 2 further illustratesvalues (arbitrary unit) of the electric potential of the auxiliaryelectrode 141 by the solid-line isogram. As can be seen from theisogram, the electric potential distribution of the auxiliary electrode141 substantially forms a concentric circle around the power feedingpoint 143 near the center of the electrode. In other words, in the casewhere the power feeding point 143 is present only at the center of theauxiliary electrode 141, the electric potential distribution of theauxiliary electrode 141 becomes non-uniform.

FIG. 3 illustrates the result of the plating thickness (the filmthickness) simulation on the substrate 131 when the auxiliary electrode141 has the electric potential distribution illustrated in FIG. 2. Thesubstrate 131 having an elongated rectangle shape with the length in theupper/lower direction of 510 mm and the lateral width of 415 mm wassimulated. Furthermore, the simulation was performed with an assumptionthat the substrate 131 was coupled to the power supply 150 along thelong side (in the entire part of the long sides) of the substrate 131.In FIG. 3, “the long sides of the substrate 131” are the left side andthe right side. Furthermore, the simulation was performed assuming thata metal to be plated is a copper. FIG. 3 illustrates a film thickness(arbitrary unit) of the copper to be plated on the substrate 131 by thesolid-line isogram. As can be seen from the isogram, the film thicknesson the substrate 131 becomes non-uniform. The film thickness becomesthickest at the center of the substrate 131 (note that parts affected bya terminal effect described later are excluded). The film thicknessbecomes thinnest at parts slightly close to the center of the substrate131 from the centers of the short sides of the substrate 131. Assumingthe film thickness at the center of the substrate 131 as 1 (a. u.), thefilm thickness at the thinnest film thickness parts became about 0.968(thinned by about 3.2%: for the film thickness, also see profiles ofFIG. 6A to FIG. 6C described later).

According to studies by the applicant, it has been found that thenon-uniformity of the plating thickness on the substrate 131 is probablycaused by the non-uniform electric potential distribution of theauxiliary electrode 141. To uniform the electric potential distribution,providing the plurality of power feeding points 143 on the auxiliaryelectrode 141 is considered to be effective.

FIG. 4 illustrates the result of the electrode potential simulation ofthe auxiliary electrode 141 when power feeding points 143 (a powerfeeding point 143A, a power feeding point 143B, and a power feedingpoint 143C) are present by three points on the auxiliary electrode 141.The respective power feeding points 143 were configured to haveidentical electric potentials. The power feeding point 143A ispositioned at the center of the auxiliary electrode 141. The powerfeeding point 143B is positioned above the power feeding point 143A. Thepower feeding point 143C is positioned below the power feeding point143A. A distance between the power feeding point 143A and the powerfeeding point 143B was configured to be one-third of the length of thelong side of the auxiliary electrode 141. A distance between the powerfeeding point 143A and the power feeding point 143C was also configuredto be one-third of the length of the long side of the auxiliaryelectrode 141. The other conditions are similar to conditions for thesimulation of FIG. 2. As can be seen from the isogram, the electricpotential distribution of the auxiliary electrode 141 in this simulationis uniformed compared with the electric potential distribution of FIG.2.

FIG. 5 illustrates the result of the plating thickness simulation on thesubstrate 131 when the auxiliary electrode 141 has the electricpotential distribution illustrated in FIG. 4. Conditions for thissimulation other than the location of the power feeding points 143 ofthe auxiliary electrode 141 are similar to the conditions for thesimulation of FIG. 3. In the simulation of FIG. 5, assuming the filmthickness at the center of the substrate 131 as 1 (a.u.), the filmthickness at the thinnest parts became about 0.996 (thinned by about0.4%: for the film thickness, also see the profiles of FIG. 6A to FIG.6C described later). In comparison with the film thickness difference(about 3.2%) in FIG. 3, the uniformity of the film thickness is greatlyimproved in FIG. 5.

For detailed comparison, FIG. 6A to FIG. 6C illustrate the profiles ofthe film thicknesses in the simulations of FIG. 3 and FIG. 5. FIG. 6Aillustrates the profiles of the film thicknesses on lines drawn from thecenters of the substrates 131 along the lateral directions. FIG. 6Billustrates the profiles of film thicknesses on lines drawn from thecenters of the substrates 131 along upper/lower directions. FIG. 6Cillustrates the profiles of film thicknesses on lines drawn from thecenters of the substrates 131 along directions toward corners of thesubstrates 131 (diagonal directions). In the simulations of FIG. 3 andFIG. 5, the film thicknesses on the substrates 131 became laterallysymmetrical and longitudinally symmetrical. Accordingly, FIG. 6A to FIG.6C illustrate the unidirectional profiles starting from the centers ofthe substrates 131. The dotted lines for which reference numerals “600”are assigned in FIG. 6A to FIG. 6C indicate the profiles of the filmthicknesses in the simulation of FIG. 3. The solid lines for whichreference numerals “601” are assigned in FIG. 6A to FIG. 6C indicate theprofiles of the film thicknesses in the simulation of FIG. 5.

The profile 600 has a downward trend in all directions of the lateraldirection, the upper/lower direction, and the diagonal direction. Inother words, the film thickness under the conditions of FIG. 3 isthinned as approaching the end portions (edges) of the substrate 131.Note that the film thickness is rapidly thinned at regions separatedfrom the end portions of the substrate 131 to some extent (regionsseparated from the end portions by about 20 to 40 mm) as approaching theend portions. Furthermore, the film thickness is considerably andrapidly thickened, as approaching the end portions, at regions adjacentto the end portions of the substrate 131 (regions within about 20 mmfrom the end portions). The parts near the end portions of the substrate131 are considered to be affected by the terminal effect.

The profile 601 is substantially horizontal (excluding the regionsaffected by the terminal effect) in all directions of the lateraldirection, the upper/lower direction, and the diagonal direction. Inother words, the film thickness under the conditions of FIG. 5 isapproximately uniform on the substrate 131.

For further detailed comparison, statistic indexes on the filmthicknesses in the simulations of FIG. 3 and FIG. 5 are shown in Table1.

TABLE 1 3 × σ/ave Range/(2 × ave) [%] [%] Simulation of FIG. 3 4.2 3.7Simulation of FIG. 5 2.7 3.5

Here, the σ indicates a standard deviation. The ave indicates an averagevalue (an arithmetic average) of the film thicknesses. The Rangeindicates (maximum value of film thickness−minimum value of filmthickness). The σ/ave indicates a coefficient of variation. TheRange/(2×ave) is an index indicative of in-plane uniformity in the filmthickness. It has been found from the statistic indexes that theuniformity in film thickness in the simulation of FIG. 5 is improvedcompared with the uniformity in film thickness in the simulation of FIG.3.

It has been proved from the above-described results of simulation thatchanging the location(s) of the power feeding point(s) 143 may changethe uniformity in the film thickness on the substrate 131. However, agreat deal of studies by the applicant have proved that the increase inthe number of power feeding points 143 does not always improve theuniformity in film thickness. Further studies by the applicant havefound conditions for the optimum location of the power feeding point143.

According to the knowledge obtained by the applicant, the optimum numberof power feeding point(s) 143 is closely associated with the area of thesubstrate 131. Furthermore, the optimum position of the power feedingpoint 143 is closely associated with the lengths of the sides of thesubstrate 131. Note that it is assumed that the substrate 131 has arectangular shape and the opposed two sides are coupled to the powersupply 150. Additionally, with the substrate 131 has an elongatedrectangle shape, it is assumed that the substrate 131 is electricallycoupled to the power supply 150 at the two long sides. A length of thesides of the substrate 131 coupled to the power supply 150 is referredto as “length L.” A length of sides of the substrate 131 not coupled tothe power supply 150 is referred to as “width W.” Moreover, it isassumed that the length L and the width W meet the following conditions.

0.8×L≤W≤L

In the following, it is assumed that the sides of the substrate 131coupled to the power supply 150 are located to be parallel to theupper/lower direction. The area of the substrate 131 is denoted by S.Additionally, the auxiliary electrode 141 may have any given size, aslong as a required power feeding point among a power feeding point143-1, a power feeding point 143-2, a power feeding point 143-3, and apower feeding point 143-4 can be provided (143-1 to 143-3 are describedlater). The auxiliary electrode 141 may preferably have the size largerthan that of the substrate 131.

The number N of power feeding points 143 is preferably determinedaccording to the area S as follows.

With 0<S≤0.14 m²: N=1

With 0.14 m²<S≤0.18 m²: N=1 or 3

With 0.18 m²<S≤0.23 m²: N=3

With 0.23 m²<S≤0.27 m²: N=3 or 5

With 0.27 m²<S≤0.29 m²: N=5

With 0.29 m²<S≤0.33 m²: N=5 or 7

With 0.33 m²<S≤0.34 m²: N=7

With 0.34 m²<S≤0.36 m²: N=7 or 9

With 0.36 m²<S: N=9

The number N of power feeding points 143 is most preferably determinedaccording to the area S as follows.

With 0<S≤0.16 m²: N=1

With 0.16 m²<S≤0.25 m²: N=3

With 0.25 m²<S≤0.31 m²: N=5

With 0.31 m²<S≤0.36 m²: N=7

With 0.36 m²<S: N=9

In the most preferred case, the conditions do not overlap with oneanother. Thus, the number N of power feeding points 143 is unambiguouslydefined. As described above, N is an odd number from 1 to 9.

When a plurality of electrodes are coupled to the auxiliary electrode141 in an almost adjacent positions, these electrodes substantially workas the single power feeding point 143. In this specification, theelectrodes substantially functioning as single power feeding point 143are regarded as “single power feeding point.” An example being regardedas “single power feeding point” includes the case of a plurality ofelectrodes with a distance between the electrodes of 30 mm or less, 20mm or less, or 10 mm or less. When the plurality of electrodes areregarded as “single power feeding point,” a center of gravity of apolygon drawn with the respective electrodes may be regarded as theposition of the power feeding point.

According to the number N of the power feeding points 143, the powerfeeding points 143 are located as illustrated in FIG. 7 FIG. 7illustrates the positions where the power feeding point 143 can beprovided. With N=1, the power feeding point 143 is provided at theposition denoted by reference numeral “143-1” in FIG. 7, that is, thecenter of the auxiliary electrode 141. Note that “the center of theauxiliary electrode 141” is not strictly limited to the center. As longas the position of the power feeding point 143-1 is within one-sixth ofthe length of the auxiliary electrode 141 along the upper/lowerdirection, the position may be displaced from the strict center in theupper/lower direction. As long as the position of the power feedingpoint 143-1 is within one-sixth of the length of the auxiliary electrode141 along the lateral direction, the position may be displaced in thelateral direction from the strict center. Here, in the case where theelectroplating apparatus 100 includes the mask 170 or a similarcomponent, “the length of the auxiliary electrode 141” does not need tobe the actual length of the auxiliary electrode 141 but may be a lengthof a part of the auxiliary electrode 141 opposed to the substrate 131via the opening 171 on the mask 170 or a similar component.

With N=3, the power feeding points 143 are provided at positions denotedby reference numerals “143-1” and “143-2” in FIG. 7. The power feedingpoint 143-2 includes two power feeding points 143-2A and 143-2B. Thepower feeding point 143-2A is positioned above the power feeding point143-1. The power feeding point 143-2B is positioned below the powerfeeding point 143-1. A distance between the power feeding point 143-1and the power feeding point 143-2A is approximately equal to a distancebetween the power feeding point 143-1 and the power feeding point143-2B, or the most preferably, the distances are completely equal.Accordingly, with N=3, the three power feeding points 143 arelongitudinally arranged.

With N=5, the power feeding points 143 are provided at positions denotedby reference numerals “143-1,” “143-2,” and “143-3.” The power feedingpoint 143-3 includes two power feeding points 143-3A and 143-3B. Thepower feeding point 143-3A is positioned to the right of the powerfeeding point 143-1. The power feeding point 143-3B is positioned to theleft of the power feeding point 143-1. A distance between the powerfeeding point 143-1 and the power feeding point 143-3A is approximatelyequal to a distance between the power feeding point 143-1 and the powerfeeding point 143-3B, or the most preferably, the distances arecompletely equal. Accordingly, with N=5, the five power feeding points143 are arranged in a cross shape.

With N=7, the power feeding points 143 are provided at positions denotedby reference numerals “143-1,” “143-2,” and “143-4.” The power feedingpoint 143-4 includes four power feeding points 143-4A, 143-4B, 143-4C,and 143-4D. The power feeding point 143-4A is positioned to the right ofthe power feeding point 143-2A and above the power feeding point 143-3A.The power feeding point 143-3B is positioned to the right of the powerfeeding point 143-2B and below the power feeding point 143-3A. The powerfeeding point 143-3C is positioned to the left of the power feedingpoint 143-2B and below the power feeding point 143-3B. The power feedingpoint 143-3D is positioned to the left of the power feeding point 143-2Band above the power feeding point 143-3B. Accordingly, with N=7, theseven power feeding points 143 are arranged in an I shape.

With N=9, the power feeding points 143 are provided at positions denotedby reference numerals “143-1,” “143-2,” “143-3,” and “143-4,” that is,all positions illustrated in FIG. 7. Accordingly, with N=9, the ninepower feeding points 143 are arranged in a rectangular grid shape ofthree lines and three rows.

The positions of the power feeding points 143 are expressible by acoordinate (x, y) when a coordinate of the power feeding point 143-1,which is positioned at the center of the auxiliary electrode 141, isdefined as (0, 0). Note that the right side in FIG. 7 is assumed as thepositive direction of x, and the upper side of FIG. 7 is assumed as thepositive direction of y. The positions of the respective points to whichthe power feeding points 143 can be set are expressed as follows.

Coordinate of the power feeding point 143-1: (0, 0)

Coordinate of the power feeding point 143-2: (0, ±C_(y))

Coordinate of the power feeding point 143-3: (±C_(x), 0)

Coordinate of the power feeding point 143-4: (±C_(x), ±C_(y))

Here, (0, ±C_(y)) is a generic term for the two points, (0, C_(y)) and(0, −C_(y)). (±C_(x), 0) is a generic term for the two points, (C_(x),0) and (−C_(x), 0). (±C_(x), ±C_(y)) is a generic term for the fourpoints, (C_(x), C_(y)), (C_(x), −C_(y)), (−C_(x), −C_(y)), and (−C_(x),C_(y)). C_(x) and C_(y) are determined by the lengths of the sides ofthe substrate 131. Specifically, C_(y) is determined by the length L ofthe substrate 131. C_(x) is determined by the width W of the substrate131.

The applicant simulated plating thicknesses of some rectangularsubstrates having the specific values, “length L” and “width W,” toobtain the optimum C_(y). The applicant has found that the relationshipbetween C_(y) and the length L is most preferably C_(y)=0.3244L+10.8.Note that the units of C_(y) and L are mm. Alternatively, C_(y) may bedetermined so as to meet the following simultaneous inequality.

$\begin{matrix}\left\{ \begin{matrix}{{{0.3244L} - 9.2} \leq C_{y}} \\{C_{y} \leq {{0.3244L} + 30.8}}\end{matrix} \right. & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

Compared with the case of the most preferred value of C_(y), for C_(y)meeting the above-described simultaneous inequality, 3×σ/ave increasesonly by about 0.5% at the maximum (Note that the comparison wasperformed assuming that the power feeding point 143-1 was positioned atthe strict center of the auxiliary electrode 141 and the value of C_(x)was the most preferred value, as described later). That is, determiningC_(y) so as to meet the above-described inequality also allows improvingthe uniformity in plating film thickness. Note that, since C_(y) is apositive value, the case where the above-described simultaneousinequality is satisfied is limited to the case of L being about 29 mm ormore.

When the applicant similarly obtained the optimum C_(x), the applicanthas found that the relationship between C_(x) and the width W is mostpreferably C_(x)=0.5727W−110.8. Note that the units of C_(x) and W aremm. Alternatively, C_(x) may be determined so as to meet the followingsimultaneous inequality.

$\begin{matrix}\left\{ \begin{matrix}{{{0.5727W} - 120.8} \leq C_{x}} \\{C_{x} \leq {{0.5727L} - 100.8}}\end{matrix} \right. & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

Compared with the case of the most preferred value of C_(x), for C_(x)meeting the above-described simultaneous inequality, 3×σ/ave increasesonly by about 0.5% at the maximum (Note that the comparison wasperformed assuming that the power feeding point 143-1 was positioned atthe strict center of the auxiliary electrode 141 and the value of theC_(y) was the most preferred value, as described above). That is,determining C_(x) so as to meet the above-described inequality alsoallows improving the uniformity in plating film thickness. Note that,since C_(x) is a positive value, the case where the above-describedsimultaneous inequality is satisfied is limited to the case of W beingabout 211 mm or more.

Note that L and W need to be values satisfying the above-described twosimultaneous inequalities and also need to meet the above-describedrelational expression (0.8×L≤W≤L). Accordingly, the minimum value of Lis about 169 mm and the minimum value of W is about 211 mm. Accordingly,the minimum value of the substrate area S becomes about 0.035 m². Notethat with N=1, since the power feeding point 143 is positioned only atthe coordinate (0, 0), the above-described two simultaneous inequalitiesdo not need to be satisfied.

The above-described procedure determines the optimum location of thepower feeding point 143 according to the area of the substrate 131, thelength L, and the width W. Optimally locating the power feeding point143 allows uniformly plating the substrate 131.

The description above premises that the sides of the substrate 131coupled to the power supply 150 are located to be parallel to theupper/lower direction. When the sides of the substrate 131 coupled tothe power supply 150 are located along a direction inclined with respectto the upper/lower direction, the use of a configuration of theauxiliary electrode 141 being similarly inclined is preferred. In otherwords, “upper/lower direction” in this specification does not alwaysindicate “vertical direction” and “lateral direction” does not alwaysindicate “horizontal direction.”

Second Embodiment

For example, as illustrated in FIG. 2, there may be a case where theelectric potential distribution of the auxiliary electrode is simulatedto examine the configuration of the electroplating apparatus. However,the electric potential distribution obtained as the result of simulationdoes not always match the actual electric potential distribution. Forbetter simulation, it could be necessary to compare the electricpotential distribution obtained as the result of the simulation with theactual electric potential distribution and optimize the conditions forsimulation.

There has been conventionally known an electroplating apparatus thatincludes a function or a mechanism to measure an average overvoltage ofthe entire auxiliary electrode. However, it was difficult for theconventional electroplating apparatus to locally measure the electricpotential of the auxiliary electrode, that is, it was difficult toobtain the electric potential distribution (an overvoltage distribution)of the auxiliary electrode. As described in the description regardingthe first embodiment, since the electric potential distribution of theauxiliary electrode affects the uniformity in plating film thickness,obtaining the electric potential distribution of the auxiliary electrodeis considerably important. Therefore, the second embodiment describes aconfiguration appropriate for the local measurement of the electricpotential of the auxiliary electrode.

FIG. 8 is a cross-sectional view illustrating the electroplatingapparatus 100 according to this embodiment. The electroplating apparatus100 of FIG. 8 further includes an auxiliary electrode holder 800 to holdthe auxiliary electrode 141 in addition to the configuration of theelectroplating apparatus 100 of FIG. 1. The shape of the substrate 131of this embodiment is not limited to the square shape but may be a shapesuch as a circular shape. The power feeding point 143 may be provided atany given position on the auxiliary electrode 141. For example, thelocation of the power feeding point 143 may be determined by the methoddescribed in the first embodiment.

The auxiliary electrode holder 800 is configured to allow disposing aplurality of reference electrodes 810. In the example of FIG. 8, thereference electrodes 810 are housed in Luggin capillaries 811. Thereference electrodes 810 have electric potentials approximatelyidentical to electric potentials near the tops of the Luggin capillaries811. Accordingly, by positioning the tops of the Luggin capillaries 811near the auxiliary electrode 141 and measuring the electric potentialsof the reference electrodes 810 by an electric potential measuringmechanism 820, the local electric potential of the auxiliary electrode141 can be measured.

In the example of FIG. 8, a potentiometer that compares and measures theelectric potentials of the respective reference electrodes 810 (that is,the local electric potential of the auxiliary electrode 141) with theelectric potential of the power supply 150 is disposed as the electricpotential measuring mechanism 820. Besides, as the electric potentialmeasuring mechanism 820, a voltmeter that measures absolute values ofthe electric potentials of the reference electrodes 810 may be employed.

FIG. 9 is a front view illustrating the auxiliary electrode holder 800according to this embodiment. In FIG. 9, the square auxiliary electrode141 held by the auxiliary electrode holder 800 is illustrated by animaginary line. Note that the shape of the auxiliary electrode 141 isnot limited to the square shape but may be other shapes such as acircular shape. The shape of the auxiliary electrode holder 800 may bechanged according to the shape of the auxiliary electrode 141. In theexample of FIG. 9, a plurality of Luggin capillary holding holes 900 areprovided on the auxiliary electrode holder 800. The respective Luggincapillary holding holes 900 are through-holes. The Luggin capillaries811 are inserted into the Luggin capillary holding holes 900 from a back(a surface not holding the auxiliary electrode 141) of the auxiliaryelectrode holder 800. While the total nine Luggin capillary holdingholes 900 are provided by three lines and three rows in FIG. 9, thenumber of Luggin capillary holding holes 900 is not limited. Increasingthe number of Luggin capillary holding holes 900 can increase themeasuring points for the electric potential.

The method for holding the Luggin capillaries 811 with the Luggincapillary holding holes 900 is merely one example. The Luggin capillaryholding hole 900 does not need to be the through-hole but may be a blindhole. As long as the electric potentials of the reference electrodes 810are measurable and the tops of the Luggin capillaries 811 can bepositioned near the auxiliary electrode 141, the Luggin capillaries 811may be held by any other holding method.

The configuration of this embodiment allows locally measuring theelectric potential of the auxiliary electrode 141 and obtaining theelectric potential distribution of the auxiliary electrode 141. Thisensures the comparison between the electric potential distributionobtained by the measurement and the electric potential distributionobtained by the simulation. Additionally, the configuration of thisembodiment allows daily monitoring the electric potential distributionof the auxiliary electrode 141 and grasping a secular change in theelectric potential distribution of the auxiliary electrode 141. Bygrasping the secular change in the electric potential distribution, afailure part in the electroplating apparatus 100 can be identified and anecessity for a maintenance work of the electroplating apparatus 100 canbe grasped.

Several embodiments of the present invention have been described abovein order to facilitate understanding of the present invention withoutlimiting the present invention. The present invention can be changed orimproved without departing from the gist thereof, and of course, theequivalents of the present invention are included in the presentinvention. It is possible to arbitrarily combine or omit respectiveconstituent elements described in the claims and specification in arange in which at least a part of the above-described problems can besolved, or in which at least a part of the effects can be exhibited.

This application discloses a method for determining a location of apower feeding point in an electroplating apparatus as one embodiment.The electroplating apparatus is configured to plate a rectangularsubstrate having a substrate area of S. The rectangular substrate hasopposed two sides coupled to a power supply. The rectangular substratehas a length L of the sides coupled to the power supply and a length Wof sides not coupled to the power supply meeting a condition of0.8×L≤W≤L. The method includes determining a number N of the powerfeeding points according to the substrate area S. The power feedingpoints are points at which an auxiliary electrode electrically contactspower feeding elements. The auxiliary electrode is configured to assistthe plating on the substrate. The power feeding element is configured tosupply the auxiliary electrode with an electric power from the powersupply.

Further, this application discloses, as one embodiment, the method fordetermining the location of the power feeding point, including,determining N in accordance with conditions of:

with 0<S≤0.14 m²: N=1;

with 0.14 m²<S≤0.18 m²: N=1 or 3;

with 0.18 m²<S≤0.23 m²: N=3;

with 0.23 m²<S≤0.27 m²: N=3 or 5;

with 0.27 m²<S≤0.29 m²: N=5;

with 0.29 m²<S≤0.33 m²: N=5 or 7;

with 0.33 m²<S≤0.34 m²: N=7;

with 0.34 m²<S≤0.36 m²: N=7 or 9; and

with 0.36 m²<S: N=9.

Further, this application discloses, as one embodiment, the method fordetermining the location of the power feeding point, including,positioning one power feeding point at a center of the auxiliaryelectrode, and further positioning the power feeding points at thefollowing respective points.

with N=3: (0, ±C_(y))

with N=5: (0, ±C_(y)) and (+C_(x), 0)

with N=7: (0, ±C_(y)) and (+C_(x), ±C_(y))

with N=9: (0, ±C_(y)), (±C_(x), 0), and (+C_(x), ±C_(y))

Here, an x-direction is a direction along the sides of the substrate notcoupled to the power supply. Here, a y-direction is a direction alongthe sides of the substrate coupled to the power supply. Here, (0,0) is acoordinate of the power feeding point located at the center of theauxiliary electrode.

Further, this application discloses, as one embodiment, the method fordetermining the location of the power feeding point, wherein

L≥169 mm, and W≥211 mm,

C_(y) using mm as a unit meets conditions of:

0.3224L−9.2≤C _(y); and

C _(y)≤0.3224L+30.8, while

C_(x) using mm as a unit meets conditions of:

0.5727W−120.8≤C _(x); and

C _(x)≤0.5727W−100.8.

The determination on the location of the power feeding point by any ofthe above-described methods makes the optimum number of power feedingpoints and/or the optimum positions possible. Optimally locating thepower feeding points allows achieving the uniform plating.

Further, this application discloses an electroplating apparatus forplating a rectangular substrate as one embodiment. The electroplatingapparatus includes a substrate holder, an auxiliary electrode, and apower feeding element. The substrate holder holds the substrate withopposed two sides among sides of the substrate. The opposed two sidesare coupled to a power supply. The auxiliary electrode is configured toassist the plating on the substrate. The power feeding element isconfigured to supply the auxiliary electrode with an electric power fromthe power supply. The rectangular substrate having a length L of thesides coupled to the power supply and a length W of sides not coupled tothe power supply meeting a condition of:

0.8×L≤W≤L;L≥169 mm; and

W≥211 mm. The power feeding element is coupled to the auxiliaryelectrode at a center of the auxiliary electrode. The power feedingelement is further coupled to the auxiliary electrode by at least onepoint among (0, ±C_(y)), (±C_(x), 0), and (±C_(x), ±C_(y)).

C_(y) using mm as its unit is a value meeting conditions of:

0.3224L−9.2≤C _(y); and

C _(y)≤0.3224L+30.8, while

C_(x) using mm as its unit is a value meeting conditions of:

0.5727W−120.8≤C _(x); and

C _(x)≤0.5727W−100.8.

Here, an x-direction is a direction along the sides of the substrate notcoupled to the power supply. Here, a y-direction is a direction alongthe sides of the substrate coupled to the power supply. Here, (0,0) is acoordinate of a coupling portion of the power feeding element with theauxiliary electrode at the center of the auxiliary electrode.

Further, this application discloses, as one embodiment, theelectroplating apparatus, wherein the substrate has a substrate area Slarger than 0.14 m² and 0.27 m² or less, and the power feeding elementsare coupled to the auxiliary electrode at three points of (0, 0) and (0,±C_(y)).

Further, this application discloses, as one embodiment, theelectroplating apparatus, wherein the substrate has a substrate area Slarger than 0.23 m² and 0.33 m² or less, and the power feeding elementsare coupled to the auxiliary electrode at five points of (0, 0), (0,±C_(y)), and (±C_(x), 0).

Further, this application discloses, as one embodiment, theelectroplating apparatus, wherein the substrate has a substrate area Slarger than 0.29 m² and 0.34 m² or less, and the power feeding elementsare coupled to the auxiliary electrode at seven points of (0, 0), (0,±C_(y)), and (±C_(x), ±C_(y)).

Further, this application discloses, as one embodiment, theelectroplating apparatus, wherein the substrate has a substrate area Slarger than 0.36 m², and the power feeding elements are coupled to theauxiliary electrode at nine points of (0, 0), (0, ±C_(y)), (±C_(x), 0),and (±C_(x), ±C_(y)).

In the above-described electroplating apparatuses, the position(s) ofthe power feeding point(s) is optimized, and thus the apparatusesprovide an effect of ensuring further uniform plating.

REFERENCE SIGNS LIST

-   -   100 . . . electroplating apparatus    -   110 . . . plating tank    -   120 . . . overflow tank    -   121 . . . circulation line    -   130 . . . substrate holder    -   131 . . . substrate    -   140 . . . auxiliary electrode unit    -   141 . . . auxiliary electrode    -   142 . . . power feeding element    -   143 . . . power feeding point    -   150 . . . power supply    -   160 . . . puddle    -   170 . . . mask    -   171 . . . opening    -   600 . . . profile of film thickness in simulation of FIG. 3    -   601 . . . profile of film thickness in simulation of FIG. 5    -   800 . . . auxiliary electrode holder    -   810 . . . reference electrode    -   811 . . . Luggin capillary    -   820 . . . electric potential measuring mechanism    -   900 . . . Luggin capillary holding hole

What is claimed is:
 1. An electroplating apparatus for plating arectangular substrate, the electroplating apparatus comprising: asubstrate holder that holds the substrate with opposed two sides of thesubstrate being coupled to a power supply; an auxiliary electrodeconfigured to assist the plating on the substrate; and a power feedingelement configured to supply the auxiliary electrode with an electricpower from the power supply, wherein the rectangular substrate having alength L of the sides coupled to the power supply and a length W ofsides not coupled to the power supply meeting a condition of:0.8×L≤W≤L, wherein L≥169 mm; and W≥211 mm, wherein the power feedingelement is coupled to the auxiliary electrode at a center of theauxiliary electrode, wherein the power feeding element is furthercoupled to the auxiliary electrode by at least one point among (0,±C_(y)), (±C_(x), 0), and (±C_(x), ±C_(y)), wherein C_(y) using mm as aunit is a value meeting conditions of:0.3224L−9.2≤C _(y); andC _(y)≤0.3224L+30.8, while and wherein C_(x) using mm as a unit is avalue meeting conditions of:0.5727W−120.8≤C _(x); andC _(x)≤0.5727W−100.8, where a direction along the sides of the substratenot coupled to the power supply is an x-direction, a direction along thesides of the substrate coupled to the power supply is a y-direction, anda coordinate of a coupling portion of the power feeding element with theauxiliary electrode at the center of the auxiliary electrode is (0, 0).2. The electroplating apparatus according to claim 5, wherein thesubstrate has a substrate area S larger than 0.14 m² and 0.27 m² orless, and the power feeding elements are coupled to the auxiliaryelectrode at three points of (0, 0) and (0, ±C_(y)).
 3. Theelectroplating apparatus according to claim 5, wherein the substrate hasa substrate area S larger than 0.23 m² and 0.33 m² or less, and thepower feeding elements are coupled to the auxiliary electrode at fivepoints of (0, 0), (0, ±C_(y)), and (±C_(x), 0).
 4. The electroplatingapparatus according to claim 5, wherein the substrate has a substratearea S larger than 0.29 m² and 0.34 m² or less, and the power feedingelements are coupled to the auxiliary electrode at seven points of (0,0), (0, ±C_(y)), and (±C_(x), ±C_(y)).
 5. The electroplating apparatusaccording to claim 5, wherein the substrate has a substrate area Slarger than 0.36 m², and the power feeding elements are coupled to theauxiliary electrode at nine points of (0, 0), (0, ±C_(y)), (±C_(x), 0),and (±C_(x), ±C_(y)).